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United States Patent |
5,757,193
|
Yu
,   et al.
|
May 26, 1998
|
Apparatus for detecting defects of wiring board
Abstract
A low-cost, fast and highly accurate defective wire detector is provided
for detecting defects of wires in a wiring board at least having one
wiring layer. The detector has a light emitting element substrate
comprising a transparent substrate and a light emitting element arranged
thereon. The light emitting element is, for example, an organic light
emitting element or an organic light emitting diode. The light emitting
element substrate is placed to be in contact with wires on a wiring board
under measurement. The detector detects and processes a condition of light
emitted from the light emitting element substrate when a voltage is
applied between the light emitting element substrate and the wiring board,
and determines whether or not any defective wire is present.
Inventors:
|
Yu; Nu (Kawagoe, JP);
Sugiyama; Tsunetoshi (Higashimatsuyama, JP);
Ogura; Shizuo (Tsurugashima, JP);
Takano; Yusuke (Tokyo, JP)
|
Assignee:
|
Hoechst Aktiengesellschaft (Frankfurt, DE)
|
Appl. No.:
|
639835 |
Filed:
|
April 26, 1996 |
Foreign Application Priority Data
| Apr 28, 1995[JP] | 7-106127 |
| Dec 04, 1995[JP] | 7-315316 |
Current U.S. Class: |
324/501; 250/559.45; 324/753 |
Intern'l Class: |
G01N 021/17; G01R 031/02 |
Field of Search: |
324/501,512,537,753
250/559.07,559.34,559.42,559.43,559.45
356/237
|
References Cited
U.S. Patent Documents
4812037 | Mar., 1989 | Riedel et al. | 324/501.
|
5270655 | Dec., 1993 | Tomita | 324/501.
|
5311137 | May., 1994 | Chang et al. | 324/501.
|
5394098 | Feb., 1995 | Meyrueix et al. | 324/750.
|
5406213 | Apr., 1995 | Henley | 324/753.
|
5598100 | Jan., 1997 | Maeda et al. | 324/501.
|
Foreign Patent Documents |
0264482 | Apr., 1988 | EP.
| |
0405737 | Jan., 1991 | EP.
| |
Other References
Kern et al., "Fluorescent Tracers-Powerful Tools for Studying Corrosion
Phenomenom and Defects in Dielectrics", vol. 43, No. 2, 1982, pp. 310-338,
XP002048671.
|
Primary Examiner: Brown; Glenn W.
Attorney, Agent or Firm: Frommer Lawrence & Haug LLP
Claims
What is claimed is:
1. An apparatus for detecting defects of wires in a wiring board including
at least one wiring layer, comprising:
a light emitting element substrate including an organic light emitting
element arranged on a transparent substrate and placed to be in contact
with wires on said wiring board to be measured, said light emitting
element substrate selectively emitting light in accordance with the
presence and absence of a defect of said wires; and
detecting means for detecting light emitted from said light emitting
element substrate to generate an output indicative of the presence of a
defect of said wires.
2. An apparatus according to claim 1, wherein:
said light emitting element substrate includes an organic light emitting
diode having a structure formed of an anode, an organic PN-junction and a
cathode laminated in this order, said organic light emitting diode
emitting light in response to an electric field applied between said anode
and said cathode causing a current to flow therethrough;
said organic PN-junction is composed of an organic P-type fluorescent
semiconductor thin film and an organic N-type fluorescent semiconductor
thin film, both said films having fluorescence; and
said organic P-type fluorescent semiconductor thin film has one surface in
contact with said anode and the other surface in contact with said organic
N-type fluorescent semiconductor thin film, respectively, and said organic
N-type fluorescent semiconductor thin film has one surface in contact with
said cathode and the other surface in contact with said organic P-type
fluorescent semiconductor thin film, respectively.
3. An apparatus according to claim 2, wherein said organic PN-junction has
a thickness ranging from 1 nm to 500 nm.
4. An apparatus according to claim 2, wherein:
said organic P-type fluorescent semiconductor thin film and said organic
N-type fluorescent semiconductor thin film satisfy the following three
conditions:
X1.ltoreq.X2
IP1.ltoreq.IP2
-0.2 eV.ltoreq.(IP2-IP1)-(X2-X1).ltoreq.0.2 eV
where X1 is an absolute value of electron affinity of said organic P-type
fluorescent semiconductor thin film, X2 is an absolute value of electron
affinity of said organic N-type fluorescent semiconductor thin film, IP1
is an absolute value of ionization potential of said organic P-type
fluorescent semiconductor thin film, and IP2 is an absolute value of
ionization potential of said organic N-type fluorescent semiconductor thin
film.
5. An apparatus according to claim 2 wherein,
said organic P-type fluorescent semiconductor thin film and said organic
N-type fluorescent semiconductor thin film each have a band gap from 1 eV
to 3.5 eV.
6. An apparatus according to claim 2, wherein said organic P-type
fluorescent semiconductor thin film is made of polyallylene vinylene
polymer expressed by:
##STR36##
wherein Ar is a substituted or non-substituted bivalent aromatic
hydrocarbon radical or a substituted or non-substituted bivalent hetero
cyclic radical, these aromatic hydrocarbon radical and hetero cyclic
radical may be condensed rings, and n is an integer equal to or more than
1.
7. An apparatus according to claim 2, wherein said organic N-type
fluorescent semiconductor thin film is made of aluminum tris(quinolinate).
8. An apparatus according to claim 1, wherein:
said organic light emitting element has one of the following structures:
(1) a structure having a light emitting layer sandwiched between an anode
and a cathode;
(2) a structure having an anode, a hole transporting layer, a light
emitting layer and a cathode laminated in this order;
(3) a structure having an anode, a light emitting layer, an electron
transporting layer and a cathode laminated in this order; and
(4) a structure having an anode, a hole transporting layer, a light
emitting layer, an electron transporting layer and a cathode laminated in
this order.
9. An apparatus according to claim 8, wherein: said anode is made of any of
nickel, gold, platinum, palladium, selenium, indium, an alloy made of any
combination of the elements including from nickel to indium, tin oxide,
ITO, copper iodide, poly(3-methylthiophene), polyphenylene sulfide and
polyaniline; and
said cathode is made of any of silver, lead, tin, magnesium, aluminum,
calcium, indium, chromium, lithium, and an alloy made of any combination
of the elements including from silver to lithium.
10. An apparatus according to claim 8, wherein said light emitting element
substrate has a dimension substantially equal to the dimension of said
wiring board.
11. An apparatus according to claim 8, wherein said defect of wires is at
least one of disconnect of any of said wires and short-circuit between
said wires.
12. An apparatus according to claim 8, wherein a voltage applied to said
wires is a DC voltage.
13. An apparatus according to claim 8, wherein said wiring board is a
printed wiring board, a liquid-crystal display panel, or a package for
integrated circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for detecting defects such as
disconnection, short-circuit and so on on a variety of wiring boards
including printed wiring boards, liquid crystal display panels, packages
for integrated circuits (IC packages), and so on.
2. Description of the Related Art
Conventionally, a variety of voltage detectors has been used to test for
disconnection, short-circuit, and so on in a predetermined portion of an
electric circuit or the like under measurement. This type of voltage
detector detects a voltage at a predetermined position on an object under
measurement by contacting a probe at the predetermined position.
However, taking printed wiring boards as an example, wiring densities on
printed wiring boards have been rapidly increased particularly at present.
More specifically, wiring patterns have been made finer, pitches between
wires have been narrowed, and an increasing number of layers have been
laminated on printed wiring boards. While wires on a throughhole mounted
device (THD) board are generally drawn at a pitch of 1.27 mm, a surface
mounted device (SMD) board requires 0.3 mm pitch for wires drawn thereon,
and a chip on board (COB) requires 0.1 mm pitch for wires drawn thereon.
The trend of increasing the density of wires on printed wiring boards may
result in increasing the occurrence of defects such as disconnect and
short circuit of wires. Thus, a need exists for a more accurate and low
cost wire testing method in a printed wiring board testing procedure.
Generally, the defects such as disconnect and short-circuit occur more
times as the number of wires increases, the wire width is reduced, and an
increased number of layers are formed on the board. Therefore, conduction
and insulation tests for printed wiring boards are indispensable steps in
order to prevent beforehand possible troubles which could be found after
electronic devices are mounted thereon.
Currently used printed wiring board testing apparatuses may be roughly
classified into two: a contact type and a non-contact type. Contact type
testing apparatuses may be again classified into two: a type which
utilizes a fixture corresponding To a printed wiring board and a flying
type which allows an operator to freely move several probe pins on a
printed wiring board for electrical testing.
With a fixture type testing apparatus, a contact probe pin having a spring
is applied with a pressure so that the probe pin is brought into contact
with a ground on a printed wiring board. Then, a predetermined bias
voltage is applied to detect a conduction situation between the ground and
each probe pin, and detected results are compared with reference data or
design data to test for defects of wires on the printed wiring board.
Since the fixture must be manufactured for each printed wiring board under
test, the fixture type testing apparatus has disadvantages that a higher
cost is required for designing and manufacturing the fixture and the
fixture Is not compatible. A further disadvantage inherent to the fixture
type testing apparatus is that it cannot be used for testing printed
wiring boards having a wiring pitch less than 0.5 mm due to a limited
accuracy of the shape of the probe pins and a pin upholding mechanism,
The flying type testing apparatus, on the other hand, is capable of testing
printed wiring boards having a wiring pitch ranging from 0.5 to 0.15 mm.
However, since the operator is required to move and contact pins at many
points on a printed wiring board under test, a test conducted by the
flying type testing apparatus takes a longer time than the fixture type
testing apparatus.
An additional disadvantage of the flying type testing apparatus is that the
testing apparatus itself is quite expensive.
Non-contact type testing apparatuses include printed wiring board
appearance testing apparatuses which conduct a test utilizing an Image of
a printed wiring board under test. The printed wiring board appearance
testing apparatuses may utilize a method of comparing an image of a
printed wiring board under test with an image of a good sample, a feature
extraction method for checking whether a pattern has been formed on a
board in accordance with a predetermined design rule, a checking method
for comparing an actual printed wiring board with CAD data, a peculiar
point recognition method, any combination of these methods, and so on.
These methods can locate narrower wires on a printed wiring board, but
cannot locate short-circuited wires.
A voltage detector utilizing an electronic beam, which is one of
non-contact type testing apparatuses, detects a voltage between wires or a
voltage between a wire and a probe and tests a printed wiring board based
on the detected voltage. Although this voltage testing apparatus can
detect a voltage without contacting a probe with a board under testing, a
portion under measurement of the board must be placed in and exposed to a
vacuum condition. In addition, there is a fear that the portion under
measurement be damaged by the electronic beam.
As liquid-crystal display panels are expected to be utilized in
increasingly wider applications, larger display sizes, higher image
qualities provided by finer-pitches, and so on have been highly demanded
for the liquid-crystal display panels, so that researches have been
actively advanced for such liquid-crystal displays which meet these
requirements. Actually, small-size and medium-size liquid-crystal display
panels have been manufactured and commercialized. For the active matrix
type liquid-crystal display panel, active elements such as transistors
functioning as switching elements, diodes and so on must be formed for all
pixels constituting a liquid-crystal display panel. Although the
manufacturing process for the formation of these active elements is
extremely complicated, the current situation has been advanced to such an
extent that active matrix type liquid-crystal display panels having more
than one million pixels have been sold in the market. For the active
matrix type liquid-crystal display panels having increasing numbers of
pixels, a reduced cost for the manufacturing process and increased yield
rate by improving the process are highly demanded.
For reducing the cost for manufacturing the liquid-crystal display panels,
it is of particular importance that defective liquid-crystal display
panels be found as early as possible. Currently, liquid-crystal display
panels are subjected to testing after liquid-crystal cells have been
formed. Thus, if a defect is found in a liquid-crystal display panel, the
defective liquid-crystal display panel is scrapped together with implanted
liquid crystals. Particularly, in the case of color displays, a defective
liquid-crystal display panel is scrapped together with a color filter
inserted therein, so that such defective liquid-crystal display panels
cause an increase in the manufacturing cost. In this sense, it is
extremely advantageous to perform a test on panels before liquid-crystals
are implanted therein in order to reduce the manufacturing cost.
Conventionally, an electrical measuring method and an optical measuring
method have been employed for testing liquid-crystal display panels. The
electrical measuring method may be a voltage measurement test using probe
pins. For example, there is an apparatus which relies on a resistance
measurement to conduct a test for disconnect and short-circuit between
respective gate lines, drain lines, and Cs bus lines by contacting the
probe pins on external connection pads or measuring pads of a thin-film
transistor (TFT) array in an active-matrix type liquid-crystal display
panel. However, with such an electrical measurement, it is absolutely
impossible to conduct a test for disconnect and short-circuit for all
pixels on an active matrix type liquid-crystal display panel having more
than one million pixels. If all pixels were tested, the test would take an
extremely long time.
An example of the optical measuring method may be a liquid-crystal display
panel visual sensing test which may be performed after liquid-crystals are
inserted between pixel electrodes and opposite electrodes of an active
matrix type liquid-crystal display panel to form cells. This measuring
method involves irradiating the surface of a liquid-crystal display panel
under measurement with light, utilizing a two-dimensional CCD sensor to
read an image of the panel in place of human's eyes, sequentially
comparing adjacent periodical patterns using pattern recognition and image
processing techniques, and detecting differences between these patterns as
defects. Since the optical measuring method is based on a test for the
appearance of a panel, it can recognize not only dust particles and
foreign substances possibly attached on the panel but also defective
patterns. However, the optical measuring method is not capable of
accurately detecting electrical disconnect and short-circuit of wires.
In addition to the foregoing measuring methods, a voltage detector
utilizing an electron beam, a measuring system utilizing a secondary
electron amount generated by a surface potential and irradiation of an
electron beam, have been practically used as non-contact type testing
apparatuses for liquid-crystal display panels. However, a liquid-crystal
display panel under measurement need be placed in a vacuum condition, and
a portion subjected to the test must be exposed thereto. Moreover, there
is a fear that the liquid-crystal display panel may be damaged by the
electron beam.
Japanese Patent Laid-open Nos. 5-240800 and 5-256794 each describe a
testing apparatus for liquid-crystal display boards utilizing an
electro-optical material or a polymer distributed liquid-crystal sheet,
The testing apparatus utilizing the electro-optical material takes
advantage of a property of the electro-optical material that its double
refractive index is changed by an electric field from a liquid crystal
display panel. Specifically, when the electro-optical material placed in
an electric field is irradiated with a laser beam, a polarization
condition of the irradiated laser beam, i.e., a phase difference between
vibration components in orthogonal two directions varies depending upon
the magnitude of the electric field. Generally, this variation in
polarization condition can be transduced into a change in electrical
magnitude by transmitting polarized light through a polarizing plate which
has a polarization direction set to a certain proper axial direction, so
that the presence or absence of defects in a liquid-crystal display panel
can be tested by observing the electrical magnitude at a certain position.
However, in general, presently available electro-optical materials are
mainly inorganic crystals such as LiNbO.sub.3 or the like. These inorganic
crystals generally have dielectric coefficients larger than the dielectric
coefficient of a space between a portion of a liquid-crystal display panel
under measurement and the inorganic crystal, i.e., the dielectric
coefficient of a layer of air, so that an electric field applied to the
inorganic crystal is reduced, thus causing a degraded measurement
sensitivity. Further, in general, an electro-optical material having a
large area cannot be actually fabricated even if either an inorganic
crystal or an organic crystal is used.
A polymer distributed liquid-crystal sheet is positioned above a
liquid-crystal display panel in a state where it is enclosed in a
transparent case. However, with such a liquid-crystal sheet, a response
speed of a testing apparatus, which depends on a response speed of
liquid-crystal molecules with respect to an electric field, is in the
order of milliseconds, so that even if fast testing is conducted, a
testing time cannot be largely reduced.
Further, when an integrated circuit having a multiplicity of terminals such
as LSI is mounted on a printed circuit board or the like, a conversion
connector is required to extend spacings between respective adjacent
terminals. Since recent high-speed clock integrated circuits generate a
significant amount of heat, many of them are enclosed in a ceramics
package which exhibits a good heat dissipation. Even integrated circuits
which do not need to dissipate so much heat are also enclosed in cheap
plastic packages. These packages for integrated circuits also tend to have
increasingly narrowing terminal pitches. While 0.3 mm pitch is currently
being used, 0.1 mm pitch is also under consideration.
For testing a conventional package for integrated circuit (IC packages)
having 0.3 mm pitch, a dedicated fixture or a flying type prober has been
used. However, the dedicated fixture must have an arrangement of pins
corresponding to the arrangement of electrodes and the number of
electrodes of a particular package, so that it lacks the versatility. In
addition, since a large number of expensive fine pins must be used, an
increased cost is inevitable. Further, it is technically difficult to
manufacture and arrange pins corresponding to a fine pitch configuration
having, for example, 0.1 mm pitch. The flying type prober, on the other
hand, differs from the fixture type one and utilizes several needle-like
probes. Thus, while the testing apparatus itself is expensive, the probes,
which are expendable supplies, are cheap. Nevertheless, it is difficult to
precisely move the probes and contact them onto small electrodes. For this
purpose, various techniques are required to accomplish this operation.
Also, since several probes must be brought into contact with electrodes,
the test requires a long time. Further, while the probes are formed in a
fine needle shape and plated with gold on the surfaces thereof so as to be
adapted to fine electrodes, it is inevitable that gold plated on
electrodes be damaged by the probes during a test. As will be understood
from the foregoing, the testing method using mechanical contact has
certain limitations. It is therefore difficult to manufacture a fixture
and pin probes corresponding to packages generally having terminals
arranged at pitches of 0.1 mm or less and to make measurements on
fine-pitch packages using such fixture and pin probes.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problems as mentioned
above. It is therefore an object of the present invention to provide a
testing apparatus for detecting defective wires on a wiring board, which
is capable of dealing with wires drawn at narrower intervals, and of
detecting conductive conditions of wires as well as locating
short-circuited wires.
It is another object of the present invention to provide a detector for
detecting defective wires on a printed wiring board.
It is a further object of the present invention to provide a testing
apparatus which is capable of dealing with small pixel areas and of
detecting disconnect, short-circuiting condition and so on for transparent
electrodes of a liquid-crystal display panel at a high detection accuracy
and without damaging the liquid-crystal panel.
It is a still further object of the present invention to provide a testing
apparatus for detecting defective wires which is capable of dealing with
IC packages having terminals arranged at narrower pitches.
To achieve the above objects, the present invention provides a detector for
detecting defective wires on a printed wiring board comprising at least
one wiring layer, which is capable of detecting such defective wires by a
combination of light emission and absence of light emission by a light
emitting element substrate positioned in contact with the printed wiring
board.
The detector comprises a light emitting element substrate including an
organic light emitting element arranged on a transparent substrate and
placed to be in contact with wires on the wiring board to be measured, the
light emitting element substrate selectively emitting light in accordance
with the presence and absence of a defect of the wires, and detecting
means for detecting light emitted from the light emitting substrate, and
is characterized by detecting the presence or absence of a defect of the
wires by an output of the detecting means.
In one embodiment of the detector, the organic light emitting element
preferably has one of the following structures:
(1) a structure having a light emitting layer sandwiched between an anode
and a cathode;
(2) a structure having an anode, a hole transporting layer, a light
emitting layer and a cathode laminated in this order;
(3) a structure having an anode, a light emitting layer, an electron
transporting layer and a cathode laminated in this order; and
(4) a structure having an anode, a hole transporting layer, a light
emitting layer, an electron transporting layer and a cathode laminated in
this order.
In another particularly preferred embodiment of the detector according to
the present invention, the light emitting element substrate includes an
organic light emitting diode having a structure formed of an anode, an
organic PN-junction and a cathode laminated in this order. The organic
light emitting diode is configured to emit light in response to an
electric field applied between the anode and the cathode to have a current
flow therethrough.
In this embodiment, the organic PN-junction is composed of an organic
P-type fluorescent semiconductor thin film and an organic N-type
fluorescent semiconductor thin film, both of the films having
fluorescence. The organic P-type fluorescent semiconductor thin film has
one surface in contact with the anode and the other surface in contact
with the organic N-type fluorescent semiconductor thin film, respectively,
and the organic N-type fluorescent semiconductor thin film has one surface
in contact with the cathode and the other surface in contact with the
organic P-type fluorescent semiconductor thin film, respectively. The
thickness of the organic PN junction may be in a range from 1 nm to 500
nm.
Preferably, the organic P-type fluorescent semiconductor thin film and the
organic N-type fluorescent semiconductor thin film satisfy all of the
following three conditions:
X1.ltoreq.X2
IP1.ltoreq.IP2
-0.2 eV.ltoreq.(IP2-IP1)-(X2-X1).ltoreq.0.2 eV
where X1 is an absolute value of electron affinity of the organic P-type
fluorescent semiconductor thin film, X2 is an absolute value of electron
affinity of the organic N-type fluorescent semiconductor thin film, IP1 is
an absolute value of ionization potential of the organic P-type
fluorescent semiconductor thin film, and IP2 is an absolute value of
ionization potential of the organic N-type fluorescent semiconductor thin
film.
The organic P-type fluorescent semiconductor thin film and the organic
N-type fluorescent semiconductor thin film each may have a band gap from 1
eV to 3.5 eV.
The organic P-type fluorescent semiconductor thin film is preferably made
of polyallylene vinylene polymer expressed by:
##STR1##
wherein Ar is a substituted or non-substituted bivalent aromatic
hydrocarbon radical or a substituted or non-substituted bivalent hetero
cyclic radical, these aromatic hydrocarbon radical and hetero cyclic
radical may be condensed rings, and n is an integer equal to or more than
1. The organic N-type fluorescent semiconductor thin film is preferably
made of aluminum tris(quinolinate).
In the foregoing two embodiments:
(1) the anode is preferably made of any of nickel, gold, platinum,
palladium, selenium, indium, an alloy made of any combination of arbitrary
elements including from nickel to indium, tin oxide, ITO, copper iodide,
poly(3-methylthiophene), polyphenylene sulfide and polyaniline;
(2) the cathode is preferably made of any of silver, lead, tin, magnesium,
aluminum, calcium, indium, chromium, lithium, and an alloy made of any
combination of arbitrary elements including from silver to lithium;
(3) the light emitting element substrate preferably has a dimension
substantially equal to the dimension of the wiring board.
(4) The defect of wires refers to at least one of disconnect of any of the
wires and short-circuit between the wires.
(5) The wiring board is applied with a DC voltage.
(6) The wiring board is either a printed wiring board, a liquid-crystal
display panel, or a package for integrated circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a conceptual diagram schematically illustrating the configuration
of a detector according to the present invention;
FIG. 2 is a diagram illustrating the configuration of a first example of a
light emitting element substrate used in a first embodiment of the
detector according to the present invention;
FIG. 3 is a diagram illustrating the configuration of a second example of a
light emitting element substrate used in the first embodiment of the
detector according to the present invention;
FIG. 4 is a diagram illustrating the configuration of a third example of a
light emitting element substrate used in the first embodiment of the
detector according to the present invention;
FIG. 5 is a diagram illustrating the configuration of a fourth example of a
light emitting element substrate used in the first embodiment of the
detector according to the present invention;
FIG. 6 is a diagram illustrating a manufacturing process of the light
emitting element substrate shown in FIG. 2;
FIG. 7 is a diagram illustrating a manufacturing process of the light
emitting element substrate shown in FIG. 3;
FIG. 8 is a diagram illustrating the structure of a light emitting element
substrate used in a second embodiment of the detector according to the
present invention;
FIG. 9A is a diagram schematically illustrating the configuration of a
first example of the detector according to the present invention;
FIG. 9B shows a positional relationship between a light emitting element
substrate of the detector and PGA;
FIG. 10A is a diagram schematically illustrating the structure of a TFT
active matrix type liquid-crystal display panel under test;
FIG. 10B is a diagram schematically illustrating the configuration of the
second example of the detector according to the present invention for
detecting defective wires on the liquid-crystal display panel; and
FIG. 10C is a diagram illustrating a light emitting pattern produced by the
detector of FIG. 10B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinafter be described in connection with its
preferred embodiments with reference to the accompanying drawings. It
should be first noted, however, that the present invention is not limited
to these specific embodiments.
FIG. 1 is a conceptual diagram schematically illustrating the configuration
of a detector according to the present invention. Referring specifically
to FIG. 1, the detector comprises a light emitting element substrate 300
in contact with wires 200 on a wiring board 100 which is subjected to a
test for determining whether defects such as short-circuit, disconnect or
the like of the wires exist. The light emitting element substrate 300
comprises a transparent substrate and a light emitting element formed on
the transparent substrate. The light emitting element substrate 300 emits
light or does not emit light in response to detection of a defect of the
wires 200. Thus, whether light is emitted or not is detected by a
detecting means 400, and processed to detect the presence or absence of a
defect of the wires 200.
The light emitting element substrate 300 is positioned in contact with the
wires 200 under measurement on the wiring board 100. Application of a
voltage to the wires 200 under measurement causes the light emitting
element substrate 300 to emit light or stop emitting light in response to
a defect of the wires 200 under measurement. Then, the detecting means 400
senses whether light is emitted or not from the light emitting element
substrate 300, for example, as an image, and determines whether or not a
defect exists on the wires 200 under measurement based on the image
sensed.
In a first embodiment of the present invention, the light emitting element
is an organic light emitting element, and the detecting means 400 includes
a detection unit and a signal processing unit. Light emitted from the
organic light emitting element Is detected by the detection unit as an
image, and the signal processing unit processes the image delivered from
the detection unit to output a signal corresponding to the presence or
absence of a defect of the wires.
FIG. 2 illustrates an exemplary structure of the light emitting element
board 300. Referring specifically to FIG. 2, the light emitting element
substrate 300 has a lamination structure in which an anode 2, a light
emitting layer 3 and a cathode 4 are laminated in this order on a
transparent substrate 1, The anode 2, light emitting layer 3 and cathode 4
form an organic light emitting element 5. As an electric field is applied
between the anode 2 and the cathode 4 to have a current pass therethrough,
the light emitting layer 3 emits light.
The transparent substrate 1 must be transparent in a range of wavelength of
the light which the light emitting element substrate 300 emits. The
transparent substrate 1 may be made of, for example, any material
belonging to a glass group such as soda glass, quartz glass, pyrex glass
or the like, and optical plastics. Although the thickness of the
transparent substrate 1 is not particularly limited, the thickness is
preferably in a range from 10 mm to 0.1 mm. Also preferably, the
transparent substrate 1 exhibits a good flatness.
A material suitable for the anode 2 deposited on the transparent substrate
1 is preferably a material having a large work function, for example,
nickel, gold, platinum, palladium, selenium, indium, alloy made of any
combination of these elements including from nickel to Indium, tin oxide,
ITO (indium tin oxide), or copper iodide. In addition, a conductive
polymer material such as poly(3-methylthiophen), polyphenylenesulfide,
polyaniline or the like may be used for the anode 2. The anode 2 must be
transparent in a range of wavelengths of light emitted from the light
emitting element substrate 300, and is preferably made of an inorganic
conductive material such as ITO, SnO.sub.2 or the like. Alternatively, a
commercially available Nesa Glass (registered Trade Mark) or the like may
be used. Preferably, the transparent anode 2 has a resistance value equal
to or less than 100 .OMEGA.cm.sup.2.
A large number of investigations have been made on materials suitable for
the light emitting layer 3, and any of such light emitting materials may
be used in the present invention. Compounds which can serve as the light
emitting materials are listed below.
Single aromatic cyclic compounds including:
(1) conventionally known anthracene, pyrene, and benzo-condensed ring
compounds expressed by the following structural formula (1) (see Japanese
Patent Laid-open No. 4-17294):
##STR2##
(2) a cumarin compound expressed by the following structural formula (2)
(see Japanese Patent Laid-open No. 3-792);
##STR3##
(3) a quinolone compound expressed by the following structural formula (3)
(see Japanese Patent Laid-open No. 3-162483):
##STR4##
and (4) pyridoimidazoquinoxaline expressed, for example, by the following
structural formula (4) (see Japanese Patent Laid-open No. 4-110390):
##STR5##
Also, the following compounds belonging to a group of condensed ring
aromatic compounds may be used:
(1) a compound having the following structural formula (5) as shown in
Japanese Patent Laid-open Nos. 5-179237 and 2-88689;
##STR6##
(2) condensed pyridine cyclic compounds such as that expressed by the
following structural formula (6) (see Japanese Patent Laid-open No.
4-161481):
##STR7##
(3) a compound expressed by the following structural formula (7) (see
Japanese Patent Laid-open No. 5-222362):
##STR8##
(4) a quinacridon compound and a quinazoline compound expressed, for
example, by the following structural formula (8) (see Japanese Patent
Laid-open No. 5-70773):
##STR9##
(5) a group of bis-oxazole compounds expressed by the following structural
formula (9) which is described in Japanese Patent Laid-open No. 5-214335:
##STR10##
(6) a pyrrolopyrrole compound expressed by the following structural
formula (10) (see Japanese Patent Laid-open No. 2-296891):
##STR11##
(7) a carboxyimide compound expressed, for example, by the following
structural formula (11) (see Japanese Patent Laid-open No. 3-177487):
##STR12##
and (8) a group of carbazole diamine compounds expressed, for example, by
the following structural formula (12) (see Japanese Patent Laid-open No.
3-35085):
##STR13##
As conjugate dyes having a olefin double bond, compounds having the
following structures may be used:
(1) a group of double-bonded aromatic compounds expressed, for example, by
the following structural formula (13) (see Japanese Patent Laid-open No.
4-264189):
##STR14##
(2) a butadiene structure as expressed by the following structural formula
(14) (see Japanese Patent Laid-open No. 4-88079):
##STR15##
and (3) a bivinyl aromatic structure as expressed by the following
structural formula (15) (see Japanese Patent Laid-open No. 4-332787):
##STR16##
Further, the following compounds belonging to oligophenylene compounds and
polyhetero cyclic compound groups may be used:
(1) an oligophenylene compound expressed by the following structural
formula (16) (see Japanese Patent Laid-open No. 3-162484):
##STR17##
(2) an oxadiazole compound expressed by the following structural formula
(17) (see Japanese Patent Laid-open No. 5-152072):
##STR18##
(3) a group of oxadiazole compounds expressed by the following structural
formulae (18), (19) (see Japanese Patent Laid-open No. 4-93388):
##STR19##
and (4) a group of bipyridine compounds expressed by the following
structural formula (20) (see Japanese Patent Laid-open No. 3-287689):
##STR20##
In addition, organic metal complex compounds as expressed by the following
general formula (21) and described in Japanese Patent Laid-open Nos.
3-289089, 5-17764, 4-85388 may also be used as compounds of another form:
##STR21##
where M represents metal, and L a ligand.
In recent years, investigations have been advanced also on light emitting
materials using polymers, and the following compounds may also be used as
a light emitting layer in the first embodiment:
(1) a side-chain polymeric compound expressed, for example, by the
following structural formula (22) (see Japanese Patent Laid-open No
4-77595):
##STR22##
(2) a disjugate main-chain polymeric compound expressed, for example, by
the following structural formula (23) (see Japanese Patent Laid-open No.
3-95291):
##STR23##
(3) a conjugate main-chain polymeric compound expressed, for example, by
the following structural formula (24) (see Japanese Patent Laid-open No.
5-247460):
##STR24##
Further, there is a host material doped with a dye, for example, aluminum
complex of 8-hydroxycumarin serving as a host material which is doped with
a fluorescent dye for laser such as cumarin or the like (J. Appl. Phys.,
Vol. 65, p. 3610, 1989). Such doped compounds may also be used in the
first embodiment.
A suitable material used for fabricating the cathode of the aforementioned
organic light emitting element may be a metal having a small work function
such as silver, lead, tin, magnesium, aluminum, calcium, indium, chrome,
lithium or the like, or a alloy made of any combination of these elements
including from silver to lithium.
Next, another example of the structure for the light emitting element
substrate 300, which may be used in the first embodiment of the detector
according to the present invention, will be described with reference FIGS.
3-5.
Referring first to FIG. 3, the light emitting element substrate 300 has a
structure including a hole transporting layer 6 sandwiched between an
anode 2 and a light emitting layer 3. While several types of materials are
currently known for the hole transporting layer 6, the hole transporting
layer 6 should be formed by a compound which is capable of efficiently
transporting holes from the anode 2 toward the light emitting layer 3 when
an electric field is applied between the anode 2 and a cathode 4. For this
purpose, a material for the hole transporting layer 6 must have a small
ionization potential and a large hole mobility as well as exhibit an
excellent stability. Specifically, such material may be a diamine
derivative which is aromatic amine. Other than the aromatic amine, a
hydrazon compound may be used.
As illustrated in FIG. 4, an electron transporting layer 7 may be
sandwiched between the light emitting layer 3 and the cathode 4. A
material for the electron transporting layer 7 must be formed of a
compound which is capable of efficiently transporting electrons from the
cathode 4 toward the light emitting layer 3 when an electric field is
applied between the anode 2 and the cathode 4. Therefore, the electron
transporting layer 7 needs to be a compound which exhibits a high electron
implant efficiency from the cathode 4 and is capable of efficiently
transporting implanted electrons. For providing these properties, the
compound must have a large electron affinity and a large electron mobility
as well as exhibit an excellent stability. Compounds which satisfy these
conditions may be aromatic compounds such as tetraphenylbutadiene (see
Japanese Patent Laid-open No. 57-51781), metal complexes such as aluminum
complex of 8-hydroxyquinoline (see Japanese Patent Laid-open No.
59-1943931 and cyclopentadiene derivative (see Japanese Patent Laid-open
No. 2-289675).
Further, as illustrated in FIG. 5, the light emitting element substrate 300
may be structured such that the hole transporting layer 6 is arranged
between the anode 2 and the light emitting layer 3, and the electron
transporting layer 7 is sandwiched between the light emitting layer 3 and
the cathode 4. In this structure, the functions of the hole transporting
layer 6 and the electron transporting layer 7 can be used in combination,
so that more efficient light emission can be accomplished.
In a second embodiment of the present invention, the light emitting element
is an organic light emitting diode, and the detecting means 400 includes a
detector unit and a signal processing unit. The detector unit detects
light emitted from the organic light emitting diode as an image, and the
signal processing unit processes the Image delivered from the detector
unit to output a signal corresponding to the presence or absence of a
defect of the wires.
In the second embodiment, the organic light emitting diode formed on a
transparent substrate comprises a structure having an anode, an organic
PN-junction and a cathode laminated in this order, wherein an electric
field is applied between the anode and the cathode to have a current flow
therethrough, causing the organic PN-junction to emit light. The organic
PN-junction is formed of an organic P-type fluorescent semiconductor thin
film and an organic N-type fluorescent semiconductor thin film both having
fluorescence. The organic P-type fluorescent semiconductor thin film has
one surface in contact with the anode and the other surface in contact
with the organic N-type fluorescent semiconductor thin film. The organic
N-type fluorescent semiconductor thin film has one surface in contact with
the cathode and the other surface in contact with the organic P-type
fluorescent semiconductor thin film, respectively.
As described above, the organic PN-junction is fabricated by laminating
P-type and N-type organic fluorescent semiconductor thin films having
different band gaps. In a thermally saturated condition, the P-type region
has the same Fermi level as the N-type region. The thermal saturation is
achieved by carriers diffusing through the junction surface, and an
internal electric field is generated in the PN-junction as a result. This
internal electric field causes a vacuum level to move and a band end to be
curved. An internal electric field generated in a conduction band between
the P-type region and the N-type region functions as a potential barrier
which prevents electrons from moving from the N-type region to the P-type
region. Similarly, an internal electric field generated in a valence band
between the P-type region and the N-type region functions as a potential
barrier which prevents holes from moving from the P-type region to the
N-type region. When a bias electric field is applied to the PN-junction in
the forward direction, electrons are implanted from the cathode to the
N-type region, while holes are implanted from the anode to the P-type
region. The electrons and holes thus implanted are accumulated on the
interface of the PN-junction. When the bias voltage exceeds a
predetermined value, the electrons enter the P-type region of the
PN-junction over the barrier formed by an internal potential and recombine
with the holes to cause light emission. Also, when the bias voltage is
equal to or higher than a predetermined value, the holes enter the N-type
region over the barrier formed by an internal potential and recombine with
the electrons to cause light emission.
The organic P-type fluorescent semiconductor thin film and the organic
N-type fluorescent semiconductor thin film, forming the organic light
emitting diode in the second embodiment; preferably have a band gap in a
range from 1 eV to 3.5 eV, respectively. This is because a wavelength band
including a visible light region from near infrared light (1240 nm) to
ultraviolet light (354 nm) can be utilized so that the detection can be
made easier.
Absolute values IP1, IP2 of ionization potentials of the organic P-type
fluorescent semiconductor thin film and the organic N-type fluorescent
semiconductor thin film forming the organic light emitting diode, and
absolute values X1, X2 of their respective electron affinities satisfy the
following three equations:
X1.ltoreq.X2 (1)
IP1.ltoreq.IP2 (2)
-0.2 eV.ltoreq.(IP2-IP1)-(X2-X1)=0.2 eV (3)
Preferably, a material for the transparent electrode serving as the anode
of the organic light emitting diode has a small work function. For
example, a polymer material having a structure expressed by the following
general formula can be used:
##STR25##
wherein Ar represents substituted or non-substituted bivalent aromatic
hydrocarbon radicals or substituted or non-substituted bivalent hetero
cyclic radicals. These aromatic hydrocarbon radicals and hetero cyclic
radicals may be condensed rings, and n in the formula is an integer equal
to or more than 1.
Polymer materials as mentioned above are preferably conductive polymer
materials of a poly(3-methylthiophene) group, a polyphenylene sulfide
group, or a polyanilene group. In addition, fluorescent dye, a polymer
material having fluorescent dye dispersed therein, or a fluorescent
polymer material may also be used. An organic P-type fluorescent
semiconductor thin film usable in the present invention has a structure
expressed, for example, by
##STR26##
wherein n is an integer equal to or more than two; or
##STR27##
where n is an integer equal to or more than 2.
Specifically, the organic P-type fluorescent semiconductor thin film is
more preferably made of polyallylene vinylene polymer, expressed by the
following formula, which can be easily formed into a thin film by a method
such as spin-coating and is thermally stable:
##STR28##
wherein Ar represents a substituted or non-substituted bivalent aromatic
hydrocarbon radical or a substituted or non-substituted bivalent hetero
cyclic radical. These aromatic hydrocarbon radical and hetero cyclic
radical may be condensed rings, and n in the formula is an integer equal
to or more than 2 and is preferably in a range from 5-30,000.
The polyallylene vinylene polymer can be synthesized by any known method.
Such a synthesizing method is described, for example, in:
(1) U.S. Pat. No. 3,706,677 issued to R. A. Wessling and R. G. Zimmerman;
(2) I. Murase et al. Synth. Net., 17.639 (1987);
(3) S. Antoun et al. J. Polym. Sci., Polym. Lett. Ed., 24,504 (1986);
(4) I. Murase et al. Polym. Commun., 1205 (1989);
(5) Japanese Patent Laid-open No. 1-79217; and
(6) Japanese Patent Laid-open No. 1-254734.
The polyallylene vinylene polymers are divided into a solvent soluble type
and a solvent insoluble type. A solvent soluble polyallylene vinylene
polymer is dissolved in an organic solvent after synthesis and refinement,
and a thin film of the solution is formed on a substrate, for example, by
spin-coating. For a solvent insoluble polyallylene vinylene polymer, a
solution of an equivalent solvent soluble chemical intermediate polymer is
used to fabricate a thin film by a film forming method such as
spin-coating, and thermally eliminated in vacuum to be converted to a
conjugate polymer.
An example of polyallylene vinylene polymer usable in the second embodiment
of the present invention may be polyphenylene vinylene polymer
(hereinafter abbreviated as "PPV") expressed by the following structural
formula:
##STR29##
The organic N-type fluorescent semiconductor thin film used in the present
invention may be formed of a fluorescent dye having an ionization
potential and an electron affinity satisfying the foregoing equations
(1)-(3), a fluorescent dye dispersed in a polymer material, or a
fluorescent polymer material, together with the organic P-type fluorescent
semiconductor thin film. For example, the organic N-type fluorescent
semiconductor thin film may be formed of a material expressed by the
following formula:
##STR30##
where n is an integer equal to or more than two; or a material expressed
by the following formula:
##STR31##
The organic P-type fluorescent semiconductor thin film and the N-type
fluorescent semiconductor thin film, forming the organic PN-junction of
the organic light emitting diode, may be fabricated by a known method, for
example, vacuum deposition, spin-coating, sputtering, sol-gel, or the
like. These organic fluorescent semiconductor thin films preferably have a
thickness of 500 nm or less from a viewpoint of the transparency and for
facilitating the manufacturing, and more preferably in a range from 10 nm
to 200 nm. Thus, the organic PN-junction may have a thickness of 1000 nm
or less, preferably in a range from 1 nm to 500 nm, and more preferably
from 20 nm to 400 nm.
Since the organic light emitting diode in the second embodiment is
fabricated as described above, an arbitrary size of the light emitting
element substrate 300 can be provided. In addition, the light emitting
element substrate can be mounted on a base which may be made of glass,
quartz, metal sheet, or any other material commonly used for a base of an
organic EL element.
In one embodiment of the detector according to the present invention,
whether light is emitted or not from the organic light emitting diodes on
the light emitting element substrate is input to the detecting means
through an optical means such as a microscope, An example of the detecting
means is a CCD camera. In this event, the light emitting element
substrate, the optical means, and the detecting means may be integrally or
separately formed. In an actual test, either of a wiring board, the
optical means and the detecting means may be moved in a plane. Within a
range of the resolution of the detecting means, the detection can be
performed without moving any component. In the detector as described, a DC
voltage ranging from 1 volt to 30 volts is applied between the anode of
the organic light emitting diode and wires on a wiring board under test.
If a wire on the wiring board under test is normal, the organic light
emitting diode will generate light corresponding to the normal portion of
the wire since the voltage is applied between the anode and the cathode of
the organic light emitting diode. The detecting means captures a
distribution of the light as image information which is displayed on a CRT
or processed by a processing unit such as a computer, whereby a
disconnected position and short-circuited position on the wires can be
known from the relationship between the distribution of light emitting
positions and the wires.
The detector according to the present invention may also be used to detect
disconnection and short-circuit in simple matrix type and active matrix
type liquid-crystal display panels. With a simple matrix type
liquid-crystal display panel, the substrate is positioned at one end of a
formed electrode and a voltage is applied from the other end. At a
disconnected position or a portion exhibiting a high resistance, the light
emitting element is not applied with the voltage, so that no light emitted
from the organic light emitting element is observed, or the luminance of
emitted light is lower than other portions. In this way, defects in a
liquid-crystal display panel can be found. On the other hand, a
short-circuited position can be also found by the same detector, utilizing
the fact that light emission is observed at a position where light would
not be emitted if short-circuit did not occur.
With an active matrix type liquid-crystal display panel, disconnected
positions and short-circuited positions can be found based on whether
light is emitted or not from an organic light emitting element when a
voltage is applied between a signal electrode and a scan electrode. For
example, if a disconnected wire exits, the voltage is not applied to a
pixel electrode beyond the disconnected position so that no light emitted
from an organic light emitting element corresponding to that position is
observed.
The detector according to the present invention can also be used to detect
defects of wires in packages for integrated circuits (IC packages) such as
PGA, PPGA, BGA and PBGA. For this purpose, the light emitting element
substrate is previously fixed so as to be in contact with wires, and the
detecting means is moved to scan the wires. For detecting disconnected
wires in an IC package, a voltage is applied to all wires in the IC
package through an all-shorting bar or through a socket for applying a
voltage to the wires. Next, the IC package is scanned by the detecting
means to detect light emitted from an organic light emitting element
thereby locating a disconnected wire. On the other hand, for detecting
short-circuited wires in an IC package, a socket for applying a voltage is
connected to pins of the IC package, and a voltage is applied to a single
wire. If the wire applied with the voltage is short-circuited with another
wire, light is emitted from an organic light emitting element
corresponding to the short-circuited position. This procedure is
sequentially repeated for all wires in the IC package, the presence or
absence of short-circuited wires can be tested for all the wires. In this
event, when the socket for applying a voltage is connected to a scanner,
the application of a voltage to each wire can be automated.
Now, a process of fabricating the light emitting element substrate 300 used
in the detector according to the present invention will be explained with
reference to FIGS. 6-8. In FIGS. 6 and 7, an organic light emitting
element is formed on a transparent substrate to fabricate the light
emitting element substrate 300, while in FIG. 8, an organic light emitting
diode is formed on a transparent substrate.
Referring specifically to FIG. 6, the light emitting element on the light
emitting element substrate 300 has a lamination structure including an ITO
layer (anode of a transparent electrode), a light emitting layer and an
Al:Mg layer (cathode). First, a glass substrate 11 of 25 mm.times.7.5
mm.times.1.1 mm in size having an ITO layer of 120 nm in thickness used as
a transparent electrode 10, is well cleansed, and polyphenylene vinylene
polymer (PPV expressed by the following structural formula (25)) is
fabricated on the transparent electrode 10 as a light emitting layer:
##STR32##
For the fabrication of the light emitting layer, 1 ml of a solvent made of
80 mg of a PPV precursor (expressed by the following structural formula
(26)) and 10 ml of methanol is spin-coated on the transparent electrode 10
at a rotational speed of 2000 rpm for 100 seconds to form a thin film 12
of the PPV precursor:
##STR33##
Then, the transparent substrate 10 with the PPV precursor thin film 12
formed thereon undergoes an elimination reaction in a vacuum oven at a
pressure of 10.sup.-5 Torr and at a temperature of 280.degree. C. to
convert the thin film 12 to a PPV thin film 13 having a thickness of 30
nm. Subsequently, a metal deposition mask having a fine pattern is placed
on the PVV thin film 13, and an alloy composed of 97% of Al and 3% of Mg
is vapor-deposited on the PPV thin film 13 at a rate of 5 angstroms/sec to
form a cathode 14 having a thickness of 150 nm. In this way, a chip having
an organic light emitting element formed on the glass substrate 11 is
fabricated. This chip is diced to have a desired size (for example, a
rectangle chip of 15.6 mm.times.16.5 mm so as to conform with the size of
PGA), thus completing the light emitting element substrate 300.
When the light emitting element substrate 300 thus fabricated was applied
with a DC voltage of 10 volts between the transparent electrode 10 and the
cathode 14, emission of yellow green light was observed. It can be
confirmed from this observation that the light emitting element substrate
300 effectively functions as an organic light emitting element.
FIG. 7 illustrates a process of fabricating another light emitting element
substrate 300. This light emitting element substrate 300 has a lamination
structure including an ITO layer (anode), a hole transporting layer, a
light emitting layer, and an Al:Mg layer (cathode).
First, similarly to the process illustrated in FIG. 6, a glass substrate 21
of 25 mm.times.7.5 mm.times.1.1 mm in size having an ITO layer of 120 nm
in thickness, used as a transparent electrode 20, is well cleansed. Next,
as the hole transporting layer, N, N'-diphenyl-N, N'-bis(3methylphenyl)-1,
1'-biphenyl-4, 4'-diamine, referred to as a triphenyl diamine derivative
(hereinafter abbreviated as "TPO"), which is expressed by the following
structural formula (27), is vapor-deposited on the glass substrate 21 at a
vacuum of 5.times.10.sup.5 Torr to form a thin film 22 having a thickness
of 50 nm:
##STR34##
Next, as the light emitting layer, a thin film 23 made of
tris(8-quinolinol) aluminum (hereinafter abbreviated as "Alq.sub.3 "),
expressed by the following structural formula (28), is fabricated:
##STR35##
For the fabrication of the light emitting layer, Alq.sub.3 is heated at a
vacuum of 10.sup.-8 Torr, and vapor-deposited on the TPD thin film 22 in a
thickness of 30 nm to form an Alq.sub.3 thin film 23. Subsequently,
similarly to the process of FIG. 6, a cathode 24 is vapor-deposited on the
thin film 23 to fabricate a chip which is then cut in an appropriate size
to complete the light emitting element substrate 300.
When the light emitting element substrate 300 thus fabricated was applied
with a DC voltage of 5 volts between the transparent electrode 20 and the
cathode 24, green light emitted from the substrate 300 was observed. It
can be confirmed from this observation that the light emitting element
substrate 300 effectively functions as an organic light emitting element.
Next, a process of fabricating the light emitting element substrate 300
used in the second embodiment of the detector according to the present
invention will be explained with reference to FIG. 8. The light emitting
element on the light emitting element substrate 300 illustrated in FIG. 8
is a hetero PN-junction organic light emitting diode having a lamination
structure including an ITO layer (anode), a PPV layer, an Alq.sub.3 layer
and an Al:Mg layer.
First, a glass substrate 31 of 25 mm.times.7.5 mm.times.1.1 mm in size
having an ITO layer of 120 nm in thickness, used as a transparent
electrode 30, is well cleansed. Then, 1 ml of a solvent made of 80 mg of a
PPV precursor and 10 ml of methanol is spin-coated on the transparent
electrode 30 at a rotational speed of 2000 rpm for 100 seconds to form a
thin film 32 of the PPV precursor. The transparent substrate 30 with the
PPV precursor thin film 32 formed thereon undergoes an elimination
reaction in a vacuum oven at a pressure of 10.sup.-5 Torr and at a
temperature of 280.degree. C. for four hours to convert the thin film 32
to a PPV thin film 33 having a thickness of 30 nm.
Next, Alq.sub.3 is heated at a vacuum of 10.sup.-6 Torr, and
vapor-deposited on the PPV thin film 33 in a thickness of 30 nm to form an
Alq.sub.3 thin film 34. Subsequently, a mask is placed on the Alq.sub.3
thin film 34, and an alloy composed of 97% of Al and 3% of Mg is
vapor-deposited on the Alq.sub.3 thin film 34 at a rate of 5 angstroms/sec
to form a cathode 35 having a thickness of approximately 150 nm. The chip
thus fabricated is cut to have a size of 15.6 mm.times.16.5 mm so as to
conform with, for example, the size of PGA, thus completing the light
emitting element substrate 300.
When this light emitting element substrate 300 was applied with a DC
voltage of 5 volts between the transparent electrode 30 and the cathode
35, a current of 0.4 mA/mm.sup.2 flowed and emission of green-yellow light
having a brightness of 240 cd/m.sup.2 emitted from the substrate 300 was
observed. The light emitting element substrate 300 exhibited a light
emitting efficiency of 0.371 m/W, with a maximum brightness being 2600
cd/m.sup.2 and a maximum absorption wavelength being at 545 nm.
Next, preferred examples of the detector according to the present invention
will be described with reference to FIGS. 9A, 9B, 10A, 10B and 10C. FIGS.
9A and 9B are diagrams for illustrating a first example of the detector
according to the present invention. Specifically, FIG. 9A illustrates the
structure of the detector using the light emitting element substrate
fabricated by the manufacturing process shown in FIG. 8 and a positional
relationship between a PGA and the light emitting element substrate when
the detector is used to test for defects of wires in a PGA which is one
type of IC packages. FIG. 9B illustrates in an enlarged view the
positional relationship between the light emitting element substrate and
the PGA.
In FIGS. 9A and 9B, the light emitting element substrate 300 has
substantially the same size as a PGA 40 under test, and a cathode 35 is
positioned to be in contact with wires in the PGA 40. For detecting a
light emitting pattern of the light emitting element substrate 300 when a
voltage is applied between the transparent electrode 30 of the light
emitting element substrate 300 and a shorting bar of the PGA, a CCD camera
(detecting means) 42 is disposed above the light emitting element
substrate 300 through a microscope (optical means) 41. The output of the
CCD camera 42 is supplied to a television monitor 43 and a frame grabber
44, and the output of the frame grabber 44 is supplied to and processed by
a computer 45. The microscope 41 and the CCD camera 42 may be provided in
an Integrated form.
In the following, the operation of the detector illustrated in FIGS. 9A and
9B will be specifically explained in connection with an example in which a
PGA 40 having wires a, b, c. d, e, f is to be tested, and a wire c is
disconnected and the remaining wires a, b and d-f are normal.
As illustrated in FIGS. 9A and 9B, with the cathode 35 of the light
emitting element substrate 300 placed in contact with the wires a-f, a DC
voltage of 10 volts is applied between the transparent electrode 30 and
the shorting bar of the PGA 40, where the transparent electrode 30 is
positioned on the positive side. Portions of the light emitting element
substrate 300 on the normal wires a, b, d-f emit light, whereas a portion
of the light emitting element substrate 300 on the disconnected wire c
does not emit light, This light emission distribution is captured as an
image signal by the CCD camera 42 through the microscope 41 and displayed
on the television monitor 43. Simultaneously, an image signal from the CCD
camera 42 is sent at real time to the frame grabber 44 which divides the
image signal by a resolution of 512.times.512 and in 256 gray levels of
gradation, and sends the resulting pattern to the computer 45. The
computer 45 analyzes the pattern on an on-line basis using image
processing software. In this way, it can be confirmed that a condition of
light emission from a portion corresponding to the wire c is different
from conditions of light emission from portions corresponding to the other
wires a, b, d-f, so that the wire c is determined to be defective.
FIGS. 10A and 10B are diagrams for explaining a second example of the
detector according to the present invention, FIG. 10A schematically
illustrates a pattern of TFT's, pixel electrodes, signal electrodes and
scan electrodes formed on a TFT active matrix type liquid-crystal display
panel 50 having an array of pixels arranged in three rows and three
columns, which is to be tested by the detector using the light emitting
element substrate 300 fabricated by the process illustrated in FIG. 8. It
is assumed herein that a wire between a pixel electrode and a TFT is
disconnected in a cell at second row and first column. FIG. 10B
schematically illustrates the configuration of a detector for testing for
defects of wires on the liquid-crystal display panel 50 by means of the
light emitting element substrate 300. The light emitting element substrate
300 has an Alq.sub.3 thin film and a cathode formed thereon which is
fabricated in a size of 20 .mu.m.times.20 .mu.m corresponding to the
pattern of the signal electrodes and the scan electrodes on the
liquid-crystal display panel 50. Similarly to FIG. 9, the light emitting
element substrate 300 has a size which covers substantially the entire
surface of the liquid-crystal display panel 50.
In FIG. 10, the light emitting element substrate 300 is registered to a
reference point using, for example, a reference pin such that it is placed
on the liquid-crystal display panel 50 corresponding to the electrode
pattern on the liquid-crystal display panel 50. Next, when a voltage is
applied between each of all signal electrodes and a corresponding scan
electrode, portions of the light emitting element substrate 300
corresponding to pixel electrodes normally connected to TFT's emit light,
whereas a portion of the light emitting element substrate 300,
corresponding to the pixel electrode in a cell at the second row and first
column, does not emit light since this pixel electrode is disconnected
with its corresponding TFT. A light emission pattern of the light emitting
element substrate 300 produced at this time is illustrated in FIG. 10C,
wherein portions of the light emitting element substrate 300 corresponding
to defect-free wires emit light. It should be noted that in FIG. 10C,
light emitting portions are marked by black. This light emitting pattern
is imaged by the CCD camera 42 through the microscope 41 to be displayed
on the television monitor 43 and simultaneously processed by the computer
45. Alternatively, the microscope 41 and the CCD camera 42 may be moved in
parallel with the light emitting substrate 300 by a scanner 51.
As will be apparent from the foregoing detailed description of the present
invention, the present invention permits the fabrication of a light
emitting element substrate corresponding to wires in a variety of shapes
and small pixels under measurement, so that the presence or absence of
defective wires can be accurately detected. Further, since the light
emitting element substrate of the present invention promptly responds to a
voltage applied thereto, the presence or absence of defective wires can be
quickly detected. Further, since the light emitting element substrate of
the present invention can be fabricated at a low cost, this light emitting
element substrate may be combined with any existing detecting means to
provide a detector at a low cost.
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